1. Field of the Invention
The present invention relates to an autofocus camera in which focus is detected by either horizontal or vertical photoelectric conversion elements which are given priority.
2. Related Background Art
A known example of such autofocus cameras is disclosed in Japanese Patent Application Laid-open No. 62-95511. This autofocus camera is described below with reference to FIG. 1.
In FIG. 1, the subject light passed through a photographic lens 1 is passed through a cross-shaped opening 2a of a field mask 2 disposed at art expected focal plane of the photographic lens 1 and then through a capacitor lens 3 and four re-projecting lenses 4 to reach an image sensor 5. Two horizontal line image sensors (photoelectric conversion elements) 5a, 5b which are extended in the horizontal direction of a camera, and two vertical line image sensors (photoelectric conversion elements) 5c, 5d which are extended in the vertical direction of the camera are disposed on the image sensor 5. The light passed through the horizontal portion of the field mask opening 2a is received by the line image sensors 5a, 5b through the corresponding reprojecting lenses 4, and the light passed through the vertical portion of the opening 2a is received by the line image sensors 5c, 5d through the corresponding reprojecting lenses 4.
The horizontal portion of the opening 2a corresponds to a horizontal detecting region 61 which is horizontally extended on the photographing image plane 60 shown in FIG. 2, and the vertical portion of the opening 2a corresponds to a vertical detecting region 62 which is vertically extended. Thus, the subject light from the horizontal detecting region 61 is received by the horizontal line image sensors 5a, 5b, and the subject light from the vertical detecting region 62 is received by the vertical line image sensors 5c, 5d.
Each of the line image sensors 5a, 5b, 5c, 5d photoelectrically converts the subject light and provides an input signal to a focus detecting circuit (not shown). The focus detecting circuit calculates defocusing amount and direction from the input signal in order to drive the photographic lens 1 to the focusing position. The photographic lens 1 is focused on the basis of the defocusing amount and direction.
The advantages of the above arrangement comprising the horizontal and vertical line image sensors are described below.
In such a focus detection system, when a subject is parallel with the direction in which two line image sensors, i.e., a detecting region in the photographing image plane, are extended, since the output of the two line image sensors is flat without contrast, the defocusing amount and direction cannot be calculated, and the focus cannot be thus detected. The line image sensors are thus disposed in both the horizontal and vertical directions so that priority is given to the line image sensors in one (for example, the horizontal direction) of the two directions for detecting focus on the basis of the output thereof, and when the focus cannot be detected, the focus is detected on the basis of the output from the line image sensors in the other direction (vertical direction). This permits the focus to be surely detected regardless of the direction in which the subject is extended.
In such conventional autofocus cameras, since the line image sensors given priority are fixed, the direction of the sensors given priority, i.e., the direction of the detecting region given priority, with respect to the subject when the camera is in the horizontal attitude is different from that in the vertical attitude. For example, when priority is given to the horizontal line image sensors (horizontal detecting region 61), the detecting region 61 given priority is extended in the horizontal direction of the subject when the camera is in the horizontal attitude, while the detecting region 61 is extended in the vertical direction of the subject when the camera is in the vertical attitude.
It will be appreciated, of course, that when focus cannot be detected by using the line image sensors given priority, the time for focusing becomes longer. Thus, when the direction of the detecting region given priority with respect to the subject changes with changes in the attitude of the camera, as described above, there is the problem that the time for focusing the photographic lens when the subject is in the vertical attitude is different from that when the same subject is in the horizontal attitude.